The typical dental office practice for preparing material for making dental impressions is to measure out alginate powder from a storage container with a measuring spoon into a mixing bowl, add water, and mix the water and alginate powder with a spatula. The alginate composition is then layered into the impression tray and used to make a dental impression. There are numerous problems with this prior art method of preparing the material used for making dental impressions. The most serious problem is the health risk resulting from a dentist, dental technician and/or the patient inhaling alginate powder during the handling of the alginate powder. When handling and mixing the powder, there is a release of powder into the air which may be inhaled by those nearby. Dentists and dental technicians run a serious risk of health problems caused by repeated inhalation of the alginate powder.
A second problem with the current typical dental office practice for making dental impressions is the difficulty of thoroughly mixing the alginate powder with water to produce a homogenous alginate mixture. When mixing water and the alginate powder with a spatula, the alginate mixture tends to entrain air within the mixture. These air bubbles and stratifications resulting from layering the composition into the impression tray decrease the quality of the impression that the alginate mixture is capable of producing. The strata can become separated in some cases, leading to poor impressions.
Another problem with the typical method of preparing material for making dental impressions is the excessive amount of time required for the complete process. The preparer must engage in numerous steps to prepare the alginate mixture. In addition, time must be taken to clean the spatula, mixing bowl, and any spilled powder after the preparation of the alginate mixture. But, because the alginate mixture tends to quickly set, the preparer is limited in the amount of time she can take mixing the alginate powder and water to help ensure thorough mixing.
U.S. Pat. No. 5,052,554, issued to Leonard, identifies certain problems with the current method of mixing together alginate powder and water in a mixing bowl. In the Leonard patent, a dental impression material package is disclosed for mixing alginate powder and water so as to eliminate the need for hand mixing alginate powder and water in a bowl. The dental impression material package of Leonard is filled with a measured amount of dental impression powder, and a frangible portion of the sealed bag is pierced by the nozzle of a syringe bulb to introduce water into the bag. The bag is then gripped at the pierced opening in the bag so that the powder in the bag can then be kneaded to mix the enclosed powder and water. When mixing is complete, a corner of the bag is cut and the mixed impression material is squeezed into the impression tray.
There are several problems with the dental impression material package of Leonard. The piercing of the bag by the syringe bulb leaves an opening in the bag that must be manually closed to prevent the contents of the bag from escaping. The need to manually close the opening in the bag makes it difficult to knead the bag, and more time may be required to fully mix the contents of the bag. Any additional time required to fully mix the powder and water within the bag will shorten the time available to the dental assistant to make the impression. In addition, because the alginate mixture begins to set so quickly, any increased time required to fully mix the contents of the bag may cause the alginate mixture to begin to set prior to the dental impression being taken.
Another problem with the dental impression material package and method of Leonard is the failure to teach a device or method for withdrawing air from the bag. Although Leonard acknowledges that air is undesirable and teaches to keep air out of the bag to the extent possible, air is still present. In particular, the addition of the water to the powder releases air from powder interstices. This excess air in the bag can result in of air becoming entrained in the alginate mixture during the mixing process so bubbles are still present.